The present invention is concerned with stability control in road vehicles using a form of video based enhancement.
A so-called Active Torque Overlay (ATO) system has been developed recently which is based on the integration of EPS, (Electronic Power Steering) and ABS/VSC (Vehicle Stability Control) and is a method for injecting torque into the steering to adjust the steering feel or to assist the driver in limit/emergency manoeuvres. In this connection a “limit manoeuvre” is one which takes place at or near the vehicle handling limits.
The following scenarios that occur at or near the vehicle handling limits are benefited by ATO:
1. Oversteer.
In the early stages of oversteer, ATO acts to assist the driver to stabilise the vehicle. ATO demands an additional assist torque of the EPS. If oversteer develops past a defined threshold then VSC acts to stabilise the vehicle through brake intervention.
2. Understeer.
In the early stages of understeer, ATO acts to feedback information to the driver about the onset of understeer. ATO adjusts the assist torque of the EPS to exaggerate the reduction of rack force as felt by the driver via the steering wheel. This control is termed understeer haptic feedback. If understeer develops past a defined threshold then VSC acts, through brake intervention, to provide a yaw moment to maintain the perceived vehicle trajectory.
3. Split-μ Braking.
During a split-μ stop, a yaw moment due to the asymmetric longitudinal braking forces is generated on the vehicle. In passive vehicles the brake pressure build up is limited to allow the driver to apply the required steering correction to maintain a desired trajectory. The ATO control however assists the driver in balancing this yaw moment by applying a torque to the steering system to assist the driver achieve the required counter moment to stabilise the vehicle. Due to the improved stability, more aggressive braking and so reduced stopping distances can be achieved.
In all these scenarios, the control systems can restore or assist in the restoration of the stability of the vehicle and/or attempt to maintain a perceived trajectory. However they cannot guarantee that the vehicle is returned to the correct direction of travel as they have no means of detecting the direction of travel. Instead, the driver necessarily corrects the direction of travel.
Video lane detection systems are known to provide a means of detecting the direction of travel of a vehicle. Such lane detection systems have been used for several Driver Assistance Systems (DAS) functions, such as Lane Departure Warning, Lane Keeping and Autonomous Cruise Control (ACC) Target Selection.